The present invention relates generally to an apparatus for exercising muscles of a human being. More particularly, the invention relates to an apparatus for causing xe2x80x9ceccentric contractionxe2x80x9d of antagonist muscles of a limb through electrical stimulation so as to apply so-called xe2x80x9cclosed-kinetic-chain exercisesxe2x80x9d for the muscles to thereby increase the strength thereof. The invention can provide a portable home gymnasium in that it is relatively small, light-weight, cost effective and easy to transport and also relatively simple in construction. In addition, the invention permits a person to receive such closed-kinetic-chain exercises in a comfortable posture and also has the effect of preventing osteoporosis in the bones.
Skeletal muscles are sources of propulsion force needed for various muscular activities and it is important to a proper functioning of the human body to maintain or increase the strength of the muscles. Paralyzed muscles of a limb become debilitated through a process known as xe2x80x9cdisuse atrophyxe2x80x9d.
Continued muscle disuse produces deterioration of the tendons and osteoporosis in the bones. Muscle debilitation also occurs when an astronaut is placed in a condition of weightlessness in outer space for a long period of time.
It has been found that debilitated muscles can be restored to near normal functioning, even after years of muscular disuse, through a physical conditioning program based on functional electrical stimulation of the muscles. Typical apparatus for electrically stimulating muscular activity includes pairs of electrodes which may be applied to the surface of the skin above the muscles to be stimulated. Such apparatus generally is designed to passively induce contraction of agonist muscles through electrical stimulation. Due to the passive nature of the electrical stimulation treatment, such systems can conveniently be used for rehabilitation of patients who are in a state of coma or who have experienced a long period of physical inactivity during which muscular deterioration has commenced.
Various types of muscular contraction are known, including (1) mecystactic contraction, (2) isometric contraction, (3) isokinetic contraction, (4) concentric contraction, and (5) eccentric contraction. The mecystactic contraction means a contraction in which muscle tension remains unchanged during contraction. The isometric contraction means a contraction in which muscle tension is increased, but the muscle is not shortened because the resistance cannot be overcome. The isokinetic contraction means a contraction in which the force of a muscle is applied during constant velocity of motion. The concentric contraction means a contraction in which the increase in tension occurs in a muscle as it shortens. Finally, the eccentric contraction means a contraction in which the increase in tension occurs in a muscle as it lengthens.
Also, there are two types of muscular exercises known in the art, including (a) open-kinetic-chain exercise and (b) closed-kinetic-chain exercise. In the open-kinetic-chain exercise, the agonist muscle works or contracts but the antagonist muscle does not work. For example, when a person seated in a chair attempts to extend a knee joint, only the quadriceps muscle which functions as an agonist muscle contracts, while the hamstring muscle functioning as the antagonist muscle does not work or is allowed to extend with the contraction of the agonist muscle. Accordingly, this open-kinetic-chain exercise is effective in strengthening only the agonist muscles.
On the other hand, the closed-kinetic-chain exercise requires both the agonist and antagonist muscles to work or contract simultaneously. For example, during squatting under the action of gravity, the agonist muscle contracts and the antagonist muscle experiences the xe2x80x9ceccentricxe2x80x9d contraction, i.e., it attempts to contract but is allowed to extend, overcoming the resistance provided by the contraction effort. Accordingly, this closed-kinetic-chain exercise can maintain and increase the strength of both the agonist and antagonist muscles.
Recent studies have revealed that the eccentric contraction is more effective in increasing the strength of muscles than any other types of muscular contraction as described above. It has also been found that the closed-kinetic-chain exercise is more efficient in strengthening muscles than the open-kinetic-chain exercise because co-contraction of the agonist and antagonist muscles results in an increased loading of the agonist muscle.
Accordingly, it is desirable to exercise muscles in an efficient and effective manner by combining the eccentric contraction and the closed-kinetic-chain exercise.
Heretofore, apparatus utilized to exercise muscles of a limb, whether it is of a mechanically loading type or an electrically stimulating type, has used a program based on the open-kinetic-chain exercise. This results in an increased strength of only the agonist muscles, necessitating subsequent and separate application of the same program for the antagonist muscles.
In recent years, various apparatus has been developed which applies the closed-kinetic-chain exercises accompanied by the eccentric contraction for muscles. In such apparatus, a mechanical loading is applied to a muscle to be exercised in a direction tending to cause flexing or extending action of the knee when the knee joint is actively extended or flexed, respectively, in opposition to such loading. Such mechanical loading type devices typically comprise oil cylinders, air cylinders, or springs, etc. and require a user to move his or her limb in a sitting posture as if rowing a boat or to work pedals during stance.
This type of apparatus for increasing the strength of muscles is particularly suited for athletes who desire to enhance their sporting capabilities and also for astronauts who need special training for weightlessness. It is also suitable for use by patients and the aged who have their muscles debilitated, if the loading is appropriately adjusted.
However, such apparatus for applying closed-kinetic-chain exercises for muscles has certain drawbacks as set forth below:
First of all, the apparatus should be equipped with additional and separate means for mechanical loading of the muscles to be exercised, which makes the entire system relatively bulky, complicated in construction and difficult to transport.
Secondly, the apparatus requires a user to assume a special, rather uncomfortable posture during exercise. For example, the user is required to move his or her limb in a sitting stance or during stance. This sometimes makes it impossible for severely injured patients to receive exercises using the apparatus.
It is, therefore, a principal object of the present invention to overcome the above-said disadvantages of the prior art devices and to provide an improved apparatus for exercising muscles in a manner which applies the closed-kinetic-chain exercise accompanied by the eccentric contraction for the muscles.
It is another object of the present invention to provide an apparatus for strengthening muscles that is relatively small, light-weight, cost effective and easy to transport and also relatively simple in construction.
It is a further object of the present invention to provide such an apparatus for strengthening muscles that does not require a user to assume a specific, rather uncomfortable, posture during exercise.
It is a still further object of the present invention to provide an improved apparatus for exercising muscles in such a manner as to prevent osteoporosis in the bones.
The present invention provides an improved apparatus for strengthening muscles, comprising first means for providing electrical stimulation to an antagonist muscle; second means for sensing a volitionally generated contraction of an agonist muscle; and third means responsive to the second means for actuating the first means to cause eccentric contraction of the antagonist muscle thereby providing resistance to the volitionally generated agonist muscle contraction. The second means provides a contraction signal indicative of contraction of the agonist muscle, and the third means is operative to actuate the first means in response to the contraction signal. The third means comprises fourth means for receiving the contraction signal from the second means and for transmitting an electric signal of muscle stimulating amplitude and waveform to the first means. The first means comprises fifth means for receiving the electric signal of muscle stimulating amplitude and waveform from the fourth means and for transmitting the electric signal to the antagonist muscle to cause eccentric contraction thereof.
The second means comprises an upper portion adapted to be placed on an upper leg portion of a leg; a lower portion adapted to be placed on a lower leg portion of the leg; and an interconnecting portion adapted to join the upper and lower portions for pivotal movement with respect to each other. The second means further comprises a goniometer operatively associated with the interconnecting portion to measure the angle at which the upper portion and lower portion make; and a sensor operatively associated with the goniometer to provide the contraction signal to the third means when the angle measured by the goniometer exceeds a predetermined threshold value.
The second means provides the contraction signal when a user in a sitting posture actively extends his knee. The fourth means is responsive to the contraction signal for transmitting the electric signal to the first means so that electrical stimulation may be provided to a hamstring muscle functioning as the antagonist muscle to cause eccentric contraction thereof. Also, the second means provides the contraction signal when a user lying with his or her face down actively flexes his knee, and the fourth means is responsive to the contraction signal for transmitting the electric signal to the first means so that electrical stimulation may be provided to a quadriceps muscle functioning as the antagonist muscle to cause eccentric contraction thereof.
These and other objects, along with various advantages and benefits of the invention, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings, which are incorporated herein and constitutes part of this specification, disclose a preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.